Ν3 Band Research Articles

Branch dependence of halfwidths: Theoretical analysis of N2-broadened halfwidths of CH3Br in the v6 band

The N2-broadened halfwidths of CH3Br in the ν6 band have been calculated, along with the relaxation matrices W. These calculations employ our modified and refined versions of the Robert-Bonamy formalism. Extensive comparisons between the predicted halfwidths from the models and experimental measurements at T = 296 K are presented. Our latest model very closely matches the measurements. Meanwhile, we considered line mixing effects in the spectral profile of the RQ(j,0) sub-branch. Our method probably yields too large values of the off-diagonal elements of W. Finally, by comparing our calculated halfwidths with the data in HITRAN, we have observed generally good agreement, especially for lines with high values of j. However, the agreement becomes poor for lines with low values of j, deteriorating as j decreases. We identified a factor contributing to this poor agreement: the neglect of branch dependence in the development of HITRAN data. We believe that for lines with low values of j, this oversight undermines the reliability of the halfwidth values of CH3Br in HITRAN.

High-resolution ro-vibrational spectrum of H[formula omitted]S in highly excited vibrational states: Re-visiting the first decade

High resolution spectra of the H232S hydrogen sulfide are re-analyzed in the region of its first decade. Thanks to the improvement of the experimental conditions (in particular, an increase in both the instrumental resolution and the effective absorption path length by 1.5 times), on the one hand, and of the use of a more correct Hamiltonian model (which additionally takes into account the interactions of the bands under study with the ν1+4ν2 and 4ν2+ν3 bands), on the other hand, the information obtained as a result of the analysis of experimental data has been significantly expanded and improved compared to the previous status. In particular, (1) the total number of assigned lines has been increased by approximately 15 percent, (2) the maximum values of quantum numbers Jmax and Kamax for the assigned lines have been increased for the studied bands in average by 20–25 percent, (3) the number of obtained ”experimental“ energy levels of the upper vibrational states (especially for the (121) and (022) vibrational states) has been significantly increased, (4) despite the increase in the number of initial vibrational–rotational energies and quantum numbers Jmax and Kamax, the value of the standard deviation drms has improved 2.7 times for the obtained upper vibrational–rotational energies.

Corrigendum to “Line parameters measurements and modeling for the ν6 band of CH3F: Generation of a complete line list for atmospheric databases”

Corrigendum to “Line parameters measurements and modeling for the ν6 band of CH3F: Generation of a complete line list for atmospheric databases”

Experimental observation of the ν1+3ν3 combination bands of 16O14N18O and 18O14N18O in the near infrared spectral region

The first observation of the ν1+3ν3 combination band of the nitrogen dioxide isotopologue 16O14N18O is presented. The band was measured using Fourier-Transform Incoherent Broad-Band Cavity Enhanced Absorption Spectroscopy (FT-IBBCEAS) in the region between 5870 cm−1 and 5940 cm−1. To confirm the assignment, the band was simulated using a standard asymmetric top Watson Hamiltonian using extrapolated rotational and centrifugal distortion constants. Furthermore, the first experimental observation of the ν1+3ν3 band of the 18O14N18O isotopologue is also reported. The positions of ro-vibrational lines of the ν1+3ν3 band of the naturally most abundant isotopologue 16O14N16O were used for wavenumber calibration of line positions.

Vibrational bands of formaldoxime isotopologue 13CD2NOH in the 280–4000 cm−1 region and rovibrational analysis of its [formula omitted] band by Fourier transform infrared (FTIR) spectroscopy

A total of 11 fundamental and 3 overtone bands of the formaldoxime isotopologue 13CD2NOH were identified using its Fourier transform infrared (FTIR) spectra which were recorded with a low resolution (0.50 cm−1) in the 500–4000 cm−1 region, and high resolution (0.00096 cm−1) in the 280–500 cm−1 region. Their relative infrared (IR) band intensities were also measured. Furthermore, a rovibrational analysis of the IR transitions of the ν12 band of 13CD2NOH was carried out using its high-resolution FTIR spectrum which was recorded at the Australian Synchrotron. A total of 1077 IR transitions of the C-type ν12 band were assigned and fitted using the Watson's A-reduced Hamiltonian in the Ir representation to derive its band center and the v12 = 1 state rovibrational constants up to all 5 quartic centrifugal distortion terms for the first time, with a root-mean-square (rms) deviation of 0.00044 cm−1. The band center of the ν12 band of 13CD2NOH were found to be 391.054446(36) cm−1. The ground state rovibrational constants up to all 5 quartic terms were determined for the first time by fitting 407 ground state combination differences (GSCDs) derived from the assigned IR transitions of the ν12 band of 13CD2NOH of this work. The rms deviation of the GSCD fit was 0.00040 cm−1. Additionally, all 3 rotational constants and 5 quartic centrifugal distortion terms of the ground state and 3 rotational constants of the v12 = 1 state of 13CD2NOH were computed from theoretical anharmonic calculations at two different levels of theory, B3LYP and MP2 with the cc-pVTZ basis set, for comparison with the experimental results. Close agreement was found for the calculated and experimental rovibrational constants of 13CD2NOH for both ground and v12 = 1 states. The vibrational anharmonic frequencies of the 12 fundamental bands of 13CD2NOH in the 280–4000 cm−1 region, and their IR band intensities were also calculated using B3LYP and MP2 with the cc-pVTZ basis set, and they were compared with the respective experimental data. Finally, the ground state rotational constants and the band center of the ν12 band of the cis conformer of 13CD2NOH were calculated and compared with those of the trans conformer of this work.

Comprehensive high resolution study of the [formula omitted]SiH[formula omitted][formula omitted] tetradecad stretching bands: Appearance and applications of the isotopic substitution effect in molecules of spherical symmetry

A set of new relations between different spectroscopic parameters of the high symmetry XY4 spherical top molecules is derived on the basis of the general isotopic substitution theory, and a comprehensive high accurate analysis of the five stretching bands (the bands ν1+ν3(F2), 2ν3(F2), 2ν3(E), 2ν3(A1), and 2ν1(A1); the three latter ones are forbidden in absorption) of the tetradecad of the SiH4 molecule is made. The high resolution spectra of MSiH4(M=28,29,30) in their natural abundance were recorded with a Bruker IFS125 HR Fourier transform infrared spectrometer at the Technische Universität Braunschweig, Germany with an optical resolution of 0.003 cm−1 and theoretically analyzed (in this case, for the first time both for all five bands of the 29SiH4 and 30SiH4 species, and for 2ν3(E), 2ν1(A1) bands of the 28SiH4 one). The number of 2713 transitions of the 28SiH4 species (which is more than fourteen times higher compared to analogous studies carried out earlier) belonging to all five ro-vibrational bands of the tetradecad (which are 272, 1897, 15, 369, and 160 transitions of the ν1+ν3(F2), 2ν1(A1), 2ν3(A1), 2ν3(F2), and 2ν3(E) bands) were assigned with the values of quantum number Jmin/Jmax = 5/22, 1/24, 14/20, 4/24, and 6/23, respectively. The analysis of the obtained experimental data was made on the basis of the Hamiltonian model which takes into account all effects and resonance interactions which are possible in such molecular system. The weighted fit of the 2713 transitions led to a set of 40 rotational, centrifugal distortion, tetrahedral splitting, and resonance interaction parameters which reproduce the initial experimental data with an accuracy of drms=4.11×10−4 cm−1. An analogous analysis was made for the two other isotopologues, 29SiH4 and 30SiH4, of silane. In this case, the initial values of the most important spectroscopic parameters of both species were theoretically estimated on the basis of results of the isotopic substitution theory. As the result of the analysis, two sets of the 12 spectroscopic parameters were obtained from the weighted fits for the 29SiH4 and 30SiH4 molecules which reproduce the 461 and 375 initial ro-vibrational transitions with the drms of 3.91×10−4 and 4.9710−4 cm−1.

CO2 ultrathin film growth on a monolayer of CO2 adsorbed on the NaCl(100) surface: sticking coefficient and IR-optical signatures in the ν3 region.

CO2 ultrathin molecular films were grown onto a preadsorbed monolayer NaCl(100)/p(2 × 1)-CO2 at 40 K. Polarization infrared spectroscopy (PIRS) reveals that so-prepared films have better quality than directly grown films. A sticking probability of 0.74 ± 0.1 was deduced from the integrated IR absorption. The presence of the monolayer doublet in the film spectra suggests a Stranski-Krastanov film growth with locally varying film thicknesses on the surface. In the region of the ν3(12C16O2) band, fine structure was observed between the well-known transverse-optical (TO) and longitudinal optical (LO) bands. Two independent computational models were applied to analyze the nature of the observed fine structure. Both pair potential calculations in combination with a vibrational exciton model as well as plane-wave density functional theory (DFT) in combination with phonon calculations of IR intensities at the Γ-point reveal that a weak mode visible in s-polarization and p-polarization originates from a vibrational film excitation located near the substrate interface. A series of p-polarized weak bands appearing and partly disappearing upon film-growth is assigned to film stacks of unique local thickness.

LED-based Fourier transform spectroscopy of 14N216O in the 9750-12050 cm−1 region

The five bands of the nitrous oxide molecule (ν1+4ν3,ν1+4ν20+3ν3, 3ν1+3ν3, ν1+5ν3 and 6ν1+2ν3) were studied in the 9750–12,050 cm−1 region using a Bruker IFS-125 M Fourier Transform Spectrometer. High brightness LEDs used as the light sources, which have provided a high signal-to-noise ratio and made it possible to record weak lines with intensities of the order of 1 × 10−26 cm/molecule at 296 K. Each spectrum was obtained by averaging over 33,120 scans. The line parameters (centers and intensities) were recovered from the observed spectra. The spectroscopic constants of the upper vibrational states together with the vibrational transition dipole moments were fitted to the measured line positions and intensities, respectively. It was found that the ν1+5ν3 band is in an interpolyad resonance anharmonic interaction with the 6ν1+2ν3 band.

Measurements of H2O-O2 line shape parameters and the determination of the intermolecular potential for modified complex Robert-Bonamy calculations

A series of spectra, one pure H2O and four H2O-O2 mixtures, were measured for the ν2 band in the 1200–1950 cm−1 region at room temperature using a single-pass copper cell housed in the Bruker 125HR high-resolution Fourier transform spectrometer (FTS) at Jet Propulsion Laboratory (JPL). All the five spectra were fit simultaneously using a multispectrum non-linear least-squares fitting software, Labfit programme suite, which adopts a speed-dependent Voigt line shape profile using full line mixing taken into account through a relaxation matrix operation. O2-broadened half-width and O2-induced frequency shift coefficients were determined for more than 350 transitions of H2 16O. These data were then checked using the smooth variation and paring rules [Brown et al. J Mol Spectrosc. 2007;246:1-21, Ma et al. Mol Phys. 2011;109:1925-41] and 186 transitions that obey the rules with less than 3% difference were chosen. Using these selected data, Modified Complex Robert-Bonamy calculations were made to determine the intermolecular potential for the H2O-O2 collision system. Some 93 potential were investigated resulting in a final potential (potential 74) that agrees with the selected half-width measurements having an average percent difference of 0.052 and a standard deviation of 5.108% between measurement and calculations.

Observation and assignment of a high-resolution FTIR-spectrum of T[formula omitted]O, DT16O and HT16O in the range of 4300 to [formula omitted

In the range of 4300 to 4700cm−1, we present analysis of the 2ν1, 2ν2+ν3 and ν1+ν3 bands of T216O, the 2ν1 and ν1+2ν2 of DT16O and the 2ν1 of HT16O. The analysed high-resolution spectrum has been obtained from a Bruker IFS 125HR Fourier-transform spectrometer with a resolution of 0.025cm−1 using an optical cell with an activity of 10GBq. For the in total 2436 lines an individual positional uncertainty of up to 3.4×10-5cm−1 and a systematic uncertainty of 7.5×10-4cm−1 could be achieved. Four of the six bands have been analysed for the first time, the ν1+ν3 band of T216O and the 2ν1 of HT16O have been analysed in previous works of our group. These datasets are extended by 527 new lines and a cross check is confirming the consistency between both works. A comparison of the assigned line positions to the variationally calculated predictions from the Tomsk database agrees with previous findings indicating that band-specific shifts and shifts depending on the rotational quantum numbers are observed leading to an overall difference of up to 0.3cm−1.

Spectral mosaics: Composite absorption cross sections of air-broadened tetrafluoromethane with comparable uncertainty in the measured intensity over orders of magnitude

We have obtained low-uncertainty absorption cross sections, together with explicit uncertainties for every wavenumber, for mixtures of tetrafluoromethane (CF4) with air at 296 K. The integrated intensities in the region of the two fundamental bands ν3 and ν4 as well as four combination bands, namely ν1 + ν4, ν2 + ν4, ν3 + ν4, and ν2 + ν3, were also evaluated. The expanded uncertainties are below 1.3 % for the fundamental and below 3 % for the combination bands. An intensity estimation for the forbidden ν1 band is also obtained. Spectral data is available online: doi: 10.7795/720.20230920.

Ozone spectroscopy in the terahertz range from first high-resolution Synchrotron SOLEIL experiments combined with far-infrared measurements and ab initio intensity calculations

Ozone is one of the important molecules in terms of the impact on the atmospheric chemistry, climate changes, bio- and eco-systems and human health. It has a strong absorption in the microwave, terahertz and far-infrared spectral ranges where a large part of the Earth’s outgoing longwave radiation to space is located. In this work, the observations, and analyses of the ozone high-resolution spectra in the THz range recorded using the Synchrotron light source of the SOLEIL CNRS equipment are reported for the first time. Thanks to the exceptional brightness of the Synchrotron radiation and to the signal/noise ratio, it was possible to observe many more ozone transitions of the cold rotational band and the hot ν2-ν2 band in the range 0.9–6 THz compared to the previous works. In addition, we have carried out new measurements and assignments for the ν2 band. The simultaneous fit of the rotational band GS-GS, the hot band ν2-ν2 and the FIR ν2 band yielded an overall weighted standard deviation of 0.68 for 13,466 line positions within the experimental accuracy. This includes all previously available MW (with the best uncertainty 0.1 – 10 kHz), FIR data and the original SOLEIL measurements that provided experimental accuracy of 0.00005 – 0.0001 cm−1 for the best lines. Significant deviations in new experimental spectra compared to available spectroscopic databases were evidenced, particularly for the line positions and energy levels at high J, Ka rotational quantum numbers that are the most pronounced in the 4.5 – 6 THz range. Accurate ab initio calculations of line intensities combined with empirically fitted line positions were used to create new linelists that permit theoretical modelling of the transmittance in a good agreement with the Synchrotron spectra in the entire range of observations for various pressures and optical paths. The region near 100 cm−1 and above appears to be more sensitive to the temperature conditions that should be considered in atmospheric observation for the currently operational and future ground based and space missions.

Optical frequency comb Fourier transform spectroscopy of formaldehyde in the 1250 to 1390 cm−1 range: Experimental line list and improved MARVEL analysis

We use optical frequency comb Fourier transform spectroscopy to record high-resolution, low-pressure, room-temperature spectra of formaldehyde (H212C16O) in the range of 1250 to 1390 cm−1. Through line-by-line fitting, we retrieve line positions and intensities of 747 rovibrational transitions: 558 from the ν6 band, 129 from the ν4 band, and 14 from the ν3 band, as well as 46 from four different hot bands. We incorporate the accurate and precise line positions (0.4 MHz median uncertainty) into the MARVEL (measured active vibration-rotation energy levels) analysis of the H2CO spectrum. This increases the number of MARVEL-predicted energy levels by 82 and of rovibrational transitions by 5382, and substantially reduces uncertainties of MARVEL-derived H2CO energy levels over a large range: from pure rotational levels below 200 cm−1 up to multiply excited vibrational levels at 6000 cm−1. This work is an important step toward filling the gaps in formaldehyde data in the HITRAN database.

High-resolution far-infrared spectroscopy and analysis of the [formula omitted] and [formula omitted] bands of chloromethane

Ro-vibrational spectra of the ν3 and ν6 bands of chloromethane (CH3Cl) were recorded in the 650–1130 cm−1 range using a Fourier transform spectrometer at the AILES beamline of the SOLEIL synchrotron facility. Two isotopologues (CH335Cl and CH337Cl) have been analyzed with the tensorial formalism developed in Dijon and a total of 6753 lines were assigned. We derived 23 tensorial parameters for the lines positions (4 for the ground state, 6 for ν3, and 13 for ν6), and 7 for the lines intensities (4 for ν3, 3 for ν6). From those parameters and self-broadening coefficients found in the literature, we simulated spectra of both isotopologues. The derived parameters were converted in the Watson formalism to be compared with a previous study. Using these results, we set up a new database of calculated chloromethane spectral lines (ChMeCaSDa).

Comparative line position and line strength analysis of the [formula omitted] dyad of [formula omitted] and [formula omitted

A highly accurate ro-vibrational analysis of FTIR spectra (line positions of 13CD4 and line strengths of both the 12CD4 and 13CD4 species) is presented. The high-resolution infrared spectra of both molecules were measured with a Bruker IFS125 HR Fourier transform infrared spectrometer at an optical resolution of 0.003 cm−1 and analyzed in the regions of 800–1400 cm−1 where the ν2/ν4 dyad is located. The number of 901 transitions with Jmax=23 were assigned to the ν4 and ν2 bands of 13CD4 (this number is about 5.3 times higher in comparison with the number of known assigned transitions for 13CD4). The weighted fit of experimental line positions was made using the Hamiltonian model which takes into account the resonance interactions between the (0001,F2) and (0100,E) vibrational states. As a result, set of 18 fitted parameters of the (0001,F2)/(0100,E) vibrational states of 13CD4 was determined which reproduce the initial 901 experimental ro–vibrational line positions with the drms=2.59×10−4 cm−1, which is close to the experimental uncertainty of the recorded spectra and about 1330 times better in comparison with the reproduction of the same line position values by the use of parameters from Loëte et al. (1983). The analysis of 1557 experimental lines of the dyad of 12CD4 and 131 lines of the dyad of 13CD4 was fulfilled with the Hartmann–Tran profile to simulate the measured line shape and to determine experimental line intensities. Sets of 6/1 varied effective dipole moment parameters of 12CD4/13CD4 are determined which reproduce the initial 1557/131 line strengths with the drms=4.80% and 4.21%. Lists of the assigned line positions and strengths in the studied region are presented as the Supplementary data to this paper.

Comparison of Raman spectral characteristics and quantitative methods between 13CH4 and 12CH4 from 25 to 400 °C and 50 to 400 bar

In recent years, increasing attention has been given to quantifying the isotopic compositions of gases by Raman spectroscopy. However, related research on the carbon isotopes of CH4 is still lacking. In this study, the Raman spectral characteristics of 13CH4 and 12CH4 in the pure CH4 system and in the CH4–H2O system are comprehensively studied at temperatures ranging from 25 to 400 °C and pressures ranging from 50 to 400 bar. For the pure CH4 system, the peak positions of the symmetric stretching band (ν1) of 13CH4 and 12CH4 both shift to a higher wavenumber with increasing temperature and decreasing pressure, and their full width at half maximum (FWHM) values can reach 4.7 cm−1 and 5.5 cm−1, respectively, with increasing temperature and density. The peak position of the ν1 band of 13CH4 is always 4.6–5.1 cm−1 lower than that of 12CH4 under the same conditions, indicating that 13CH4 and 12CH4 can be distinguished by peak position and FWHM in the Raman spectra. Although the calculated Raman shifts (ν0) at zero-density for 13CH4 and 12CH4 are different, the unified equation for determining the density of CH4-rich fluid inclusions is still applicable, as long as to bracket the sample measurement with measurements of reference standards. For the CH4–H2O system, the peak position of the ν1 band of dissolved 13CH4 is approximately 2.5 cm−1 lower than that of 12CH4, while their FWHM values can be more than 12.2 cm−1, causing more difficulty in distinguishing them in aqueous solutions. In addition, Raman quantitative calibration models of 12CH4 and 13CH4 in the CH4–H2O system are established. The difference in the Raman scattering cross section (RSCS) of dissolved 12CH4 and 13CH4, rather than changes in the molar density or RSCS of water is the main reason leading to the difference in the Raman quantitative calibration models of CH4 concentrations between the 12CH4–H2O system and the 13CH4–H2O system. Our work provides a good reference for the in situ identification and quantification of the carbon isotopic composition of CH4 in high-temperature and high-pressure environments.

Analysis of line positions of the ν6 band of 35ClNO2 around 411 cm−1

The first investigation of the ν6 band of the 35ClNO2 isotopic species of nitryl chloride, located at 410.11824 (± 0.00007) cm−1 has been performed using a high resolution (0.00102 cm−1) Fourier transform spectrum recorded at the SOLEIL synchrotron source. This B-type band is rather weak but a long optical path was used and, during the spectrum recording, the nitryl chloride sample was kept at low temperature (221 K) in the optical cell. In this way, the rather strong ν2–ν3 difference band located at 422.6 cm−1, observed at 296 K during a previous investigation of the far infrared region [Orphal J, Morillon-Chapey M, Klee S, Mellau GC, Winnewisser M. J Mol Spectrosc 1998;190:101–6], and interfering with observation, could be strongly reduced. This first assignment of the ν6 band of 35ClNO2 was pursued up to high J and Ka quantum number values, J = 79 and Ka = 37. The ν6 band (expected to be of B-type) has a clearly unusual line intensity pattern, since the P branch is about twice as strong as the R-branch. Since the (weak) ν6 band is located close by to the strong A-type ν3 band located at 370 cm−1 [Anantharajah A, Kwabia Tchana F, Manceron L, Orphal J, Flaud JM. J Quant Spectrosc Radiat Transf 2020; 253:107,078], one could reasonably expect that the ν6 band borrows part of its intensity through the existence of a C-type Coriolis resonance that couples together the 61 ⇔ 31 interacting energy levels. However, during the 61 energy level computation, we could not evidence such resonance, and only a classical Watson's type A-type reduced rotational Hamiltonian, involving a single upper state, was used for this calculation.

Joint survey of the experimental high-resolution spectra of H16O37Cl and H16O35Cl with a reanalysis of the [formula omitted] band

The study starts with a detailed analysis of all the high-resolution rovibrational transitions measured for the minor hypochlorous acid isotopologue H16O37Cl, employing the Marvel (Measured Active Rotational-Vibrational Energy Levels) procedure. The survey considers 16 sources, the wavenumber coverage of the transitions extends from the microwave to the visible region, corresponding to 13 vibrational parent states. Experimental transitions data from older (1994, 1996, and 2000) sources, not published explicitly in the original papers, are presented in here for the first time; the newly reported transitions represent about one third of all the transitions assigned for H16O37Cl. Then a minor update to the transitions and levels of H16O35Cl published in J. Mol. Spectrosc. 384 (2022) 111561 is provided. Proper labelling and internal consistency of the transitions and the empirical rovibrational energies of H16O35Cl and H16O37Cl is enforced utilizing effective Hamiltonian (EH) and first-principles variational nuclear-motion computation results. An iteratively updated line list, based on empirical and EH rovibrational energy levels and first-principles intensities, is used to assign a significant number of new transitions in the 2ν2 band (2300–2800 cm−1) for both isotopologues. At the end, for H16O35Cl/H16O37Cl, from the total of 20349/10266 experimentally measured transitions considered, 20119/10124 could be validated, allowing the derivation of 5760/3933 empirical rovibrational energy levels with well-defined uncertainties. Improved parameters for an effective Hamiltonian corresponding to the 2ν2 state are given. A comparison with data in the canonical spectroscopic line-by-line database HITRAN is also provided.

Improved Theory of the Effective Dipole Moments and Absolute Line Strengths of the XY2 Asymmetric Top Molecules in the X2B1 Doublet Electronic States.

A new effective dipole moment model for the XY2 (C2v-symmetry) molecule in a doublet electronic state is derived that includes (as special cases) all currently known models of effective dipole moments for such types of molecules, and allows us to take into account the influence of spin-rotation interactions on the effective dipole moment operator that were not considered in the preceding studies. Necessary for the analysis of absolute line strengths, the matrix elements of this dipole moment operator are derived. A comparison with the previous analog models is made and discussed. The efficiency of the obtained results is illustrated, which have been applied to a set of the "forbidden" ΔKa=2 transitions of the ν3 band of the OClO free radical molecule.

The Vibrational-Rotational High-Resolution Spectrum in the Region of 3ν4, ν2 + 2ν4 and 2ν2 + ν4 Bands of the 72GeH4 Molecule

The Vibrational-Rotational High-Resolution Spectrum in the Region of 3ν4, ν2 + 2ν4 and 2ν2 + ν4 Bands of the 72GeH4 Molecule